Regulation of retinal vascular endothelial growth factor and receptors in rabbits exposed to hyperoxia.

PURPOSE: To evaluate the molecular responses of vascular endothelial growth factor (VEGF) and its receptors to dexamethasone (Dex) and celecoxib (Cel) during hyperoxia and during hyperoxia followed by recovery in room air, in newborn rabbit retinas. METHODS: Newborn rabbits at 3 days postnatal age (n = 96) received room air or oxygen (80%-100%) for 4 days, during which they were administered saline (Sal), Dex, vehicle (Veh), or Cel (n = 12/treatment group). Six animals from each group were killed immediately after hyperoxia (or room air) and the remainder exposed to room air for 5 days. Retinal mRNA expression of VEGF(121), VEGF(165), VEGF receptor-1 (VEGFR-1, or Flt-1), and VEGFR-2 (or KDR/Flk-1) was determined. RESULTS: Hyperoxia resulted in increased retinal expression of mRNA of the VEGF splice variants in the groups treated with Sal, Dex, and Veh, whereas a decrease in VEGF(121) was noted in the Cel-treated group. In contrast, retinal Flt-1 receptor mRNA was markedly increased in the Cel-treated group only, whereas retinal VEGFR-2 (KDR/Flk-1) receptor mRNA was suppressed in all the treatment groups. Hyperoxia followed by recovery in room air resulted in a minimal decrease in expression of retinal Flt-1 mRNA in the Sal and Dex groups. Cel treatment abolished its expression. CONCLUSIONS: The findings of increased retinal expression of VEGF mRNA in the newborn rabbit in response to hyperoxia are most likely due to species differences. Selective targeting of VEGF(121) and Flt-1 mRNA by Cel may represent one regulatory pathway for their anti-inflammatory effects. Further studies are needed to evaluate the therapeutic benefits of cyclooxygenase (COX)-2 inhibitors for the treatment and/or prevention of diseases associated with neovascularization.

Differential regulation of prostacyclin and thromboxane by dexamethasone and celecoxib during oxidative stress in newborn rabbits.

To compare the effects of dexamethasone (Dex) and celecoxib (Cel) on F-isoprostane, prostacyclin (PGI2), and thromboxane A2 (TxA2) following hyperoxia, and hyperoxia followed by recovery in room air (RA), newborn rabbits were exposed to hyperoxia (80-100% oxygen) for 4 days, during which they were treated with saline (Sal, i.m.), Dex (i.m.), vehicle (Veh, PO), or Cel (PO, n = 12 per group). Six animals in each group were sacrificed immediately following hyperoxia, and the remainder allowed to recover in RA for 5 days. The control litters were treated simultaneously in RA with all conditions other than atmospheric oxygen being identical. Blood samples were assayed for 8-epi-prostaglandin F2alpha (8-epi-PGF2alpha), 6-keto prostaglandin F1alpha (6-ketoPGF1alpha), and TxB2. Dex and Cel decreased 8-epi-PGF2alpha during hyperoxia and the recovery period. Dex increased 6-ketoPGF2alpha following hyperoxia, while similar increments were noted during recovery with Cel. Although TxB2 was decreased only during the recovery period, TxB2/6-ketoPGF1alpha ratio was lower during hyperoxia and recovery in both treated groups. The effect of Cel on 8-epi-PGF2. and TxA2/PGI2 ratio confirm the formation of a COX-derived F2-isoprostane that is possibly linked to TxA2 receptors. Further studies are required to examine whether Cel can be used as a therapeutic alternative to Dex for oxygen-induced injury in the newborn.

Early postnatal dexamethasone influences matrix metalloproteinase-2 and -9, and their tissue inhibitors in the developing rat lung.

In order to test the hypothesis that early postnatal exposure to dexamethasone (Dex) influences matrix metalloproteinases (MMP)-2 and -9, as well as their tissue inhibitors (TIMP-1 and -2) in the developing rat lung, newborn rats (3 litters/group) were treated with low Dex (0.1 mg/kg/day, IM), high Dex (0.5 mg/kg/day), or equivalent volumes of saline at 5 days postnatal age (P5), P6, and P7. Lung weight and lung MMP and TIMP levels were determined at sacrifice (7 days postinjection, P14; at weaning, P21; and at adolescence, P45, n = 10/group and time). Dex did not adversely affect lung weight or lung MMP-2 levels, which peaked in all groups at P21 and then fell by P45. In contrast, Dex decreased TIMP-2 at all time intervals, but achieved statistical significance only at P45. An imbalance in MMP-2/TIMP-2 ratio was noted at P21, with elevations occurring in the low and high Dex-treated groups. Lung MMP-9 levels remained comparable with controls during low Dex treatment. However, high Dex exposure resulted in elevated lung MMP-9 levels at P21 and P45. Lung TIMP-1 levels increased only with high Dex exposure at P14 and P21, whereas the lung MMP-9/TIMP-1 ratio was elevated at P21 in the high Dex group, and at P45 in both Dex-treated groups. These data provide evidence that early postnatal dexamethasone results in an imbalance between gelatinase-A and -B, and their tissue inhibitors in the developing rat lung. These changes may be responsible, in part, for some of the known maturational effects of steroids on lung structure in the newborn.